Run external Javascript on given URL?

I want to be able to write javascript that executes on a page that I visit every day. It is for my employers blog-like "What's New" page where there are announcements such as new hires, terminations, etc. But among these are also article that announcing grants we received and other important things.

I want to filter out th开发者_运维百科ose things that I don't care about but keep those that I do. I could do this with CSS if there were selectors that I could match on. But there are none that seperate those posts from the ones I don't care about.

So, is there a way in Firefox to specify a js file that would act on a certain URL? Like there is a user defined userChrome.css that matches on all CSS in a page?

Thanks Eric

You want Greasemonkey. Despite the name that makes you go ewwwww, it is a very powerful and useful tool.